1. Field of the Invention
This invention is directed to the discovery that certain cholesteryl and cholestanyl esters of anthracene analogues, and derivatives thereof, in small quantities, produce stable, thermally reversible gels of organic solvents. The invention relates to the process of gelling organic solvents utilizing the anthracene analogue cholesteryl and cholestanyl esters and derivatives, to the gelled organic solvent compositions which are produced by the process, and to novel anthracene analogue cholesteryl and cholestanyl esters and derivatives for producing same.
2. Background of Related Technology
Gelation is one of the common forms of colloidal behavior, with gels having been prepared for many substances. Gelled forms of organic solvents are of particular interest, with attention currently being focused on controlling the flammability of a large variety of organic solvents in order to significantly reduce fire hazard and improve the handling characteristics of the organic solvents. The patent literature is replete with technology directed to gelling agents for organic solvents.
Weissberger et al., U.S. Pat. No. 2,388,887, disclose the use of 2-alkyl-substituted 1,4-dihydroxybenzene compounds as agents for producing stiff gels with liquid aliphatic hydrocarbons and liquid halogenated aliphatic hydrocarbons.
Hill et al., U.S. Pat. No. 2,751,284, disclose "bodying agents" for gelling normally liquid hydrocarbons and other organic liquids. The gelling agents disclosed by Hill et al. are a 2-component composition, the first liquid composition comprising an aluminum alkoxide in toluene or other aromatic hydrocarbon of high solvency power, and the second liquid composition comprising a mixture of a low molecular weight ketone, water, and C.sub.6 -C.sub.18 fatty acids, preferably isooctanoic acids.
Kelly et al., U.S. Pat. No. 3,084,033, disclose thicknened, normally liquid hydrocarbons which are useful as fuel or the charge in certain devices such as incendiary missiles, flame throwers, rockets, portable cooking stoves, and the like. The Kelly et al. process comprises mixing the normally liquid hydrocarbons with a very small proportion of solid, crystalline polypropylene. Surprisingly, according to Kelly et al., while propylene functions in the disclosed invention, polymers of other olefins, such as polyethylene and polybutenes were found to be completely ineffective. On the other hand, Sarem, U.S. Pat. No. 3,507,635, discloses gelled jet fuels produced by adding polyisobutylene, the resulting gel capable of being fluidized by high speed shearing, the fluidized gel then suitable for pumping to a jet engine as a fluid.
Hiatt et al., U.S. Pat. No. 3,545,946, disclose petroleum distillate fuel compositions in gelled form, said compositions gelled at room temperature and liquid at elevated temperatures of about 55.degree. C. and above. The gelled compositions comprise 75-95 weight percent of a petroleum distillate fuel and from 5 to about 25 weight percent of a paraffinic hydrocarbon gelling agent containing from about 25 to about 35 carbon atoms per molecule and melting the range of about 140.degree. F. to about 155.degree. F.
Jones et al., U.S. Pat. No. 3,692,504, disclose the production of gelled compositions containing gasoline and other normally liquid hydrocarbons such as benzene, toluene, xylenes, kerosene, naphthas, and the like, said compositions gelled by a process comprising dissolving a synthetic elastomer in a normally liquid hydrocarbon and treating the resulting solution with sulfur dioxide in the presence of a suitable catalyst, i.e., typically, nitrates of the alkali metals, peroxides, hydroperoxides, and the like.
Iwama et al., U.S. Pat. No. 3,807,973, disclose gelled hydrocarbon fuels prepared by gelling the hydrocarbon fuel with a fatty acid diethanolamide, diethanolamine, a fatty acid triethanolamine ester, or a triethanolamine. The Iwama compositions purportedly have the advantage that the gelled hydrocarbons are highly stable, have substantially reduced fluidity, and still retain their desirable burning quality as fuels for heating means, reciprocating engines, diesel engines, jet engines, and the like.
Teng et al., U.S. Pat. No. 3,824,085, disclose esters of hydroxypropyl cellulose and hydroxypropyl starch useful as gelling agents for organic solvents, the gelling agents particularly useful in gelling methylene chloride (useful in paint stripping) and ethyl bromide (useful as soil fumigants). The hydroxypropyl cellulose laurate derivative is disclosed as particularly useful as a gelling agent for jet fuel.
Teng et al., U.S. Pat. No. 3,960,514, improved upon the invention of Teng et al. ('085, supra) by providing a gelled jet fuel having incorporated therein hydroxypropyl cellulose laurate and a synergistic additive comprising an elastic, high molecular weight, synthetic polymer.
Tarpley, U.S. Pat. No. 4,156,594, discloses a thixotropic gel fuel composition comprising 5 to about 75 volume percent of a solid carboniferous combustible material suspended in a liquid fuel and about 1 to about 10 weight percent of a substantially completely combustible gelling agent, said combustible gelling agent selected from the group consisting of natural and synthetic gums, resins, modified castor oil polymers, and the like.
Other gelling agents have been used for organic liquids as well. Saito et al., U.S. Pat. No. 3,969,087, disclose the use of a small amount of N-acyl amino acids or derivatives thereof, such as esters, amides, and amine salts of the N-acyl amino acids, as gelling agents for nonpolar organic liquids.
Vaterodt, U.S. Pat. No. 2,719,782, discloses the formation of gels from solvents such as hexane, heptane, octane, terpenes, sesqui-terpenes, benzene, ethyl acetate, and the like, including essential oils for use in the perfume industry. The gelling agent disclosed by Vaterrodt comprised lanosterol, prepared by saponifying wool grease with sodium hydroxide, thereafter removing the lanoline acids as the insoluble calcium salt, and removing the lanolin alcohols by a suitable solvent such as acetone. The lanosterol was obtained from the lanolin alcohol filtrate by precipitation with acetone and methanol. The gelled hydrocarbons of Vaterrodt comprised 8-15% of lanosterol.
Terech, P. et al., J. Physique 46: 895-903 (1985) presented the results of a Small Angle Neutron Scattering (SANS) study of a gel formed by a dilute solution (less than one weight percent solution) of a paramagnetic modified steroid, 3-beta-hydroxy-17,17-dipropenyl-17a-aza-D-homoandrostanyl-17a-oxy in cyclohexane.
Tachibana, T. et al., Bull. Chem. Soc. Jpn. 53: 1714-1719 (1980), describe optically active 12-hydroxyoctadecanoic acids which form thermally reversible gels with aromatic solvents or carbon tetrachloride. The authors further discussed the work of Samulski, E. T. et al., "Liquid Crystals and Plastic Crystals," Ed. by G. W. Gray and P. A. Winsor, Ellis Horwood, Chichester, pp. 175-198 (1974), who purportedly described a cholesteric mesophase formed by synthetic polypeptides in organic solvents.
However, in spite of the substantial amount of work devoted to developing gelled organic solvents, a need has continued to exist for highly stable, thermally reversible, gelled organic solvents, particularly for use as fuels, wherein the gelling agent is present in a small percentage and does not function as an impurity in the combustion process.